184 TRANSACTIONS OF THE ILLINOIS 



Residing chiefly on the leaf or leaf-stalk, and forming true galls, in 

 which they are hid from view — Pemphigus, Thalaxes, Hormaphis and 

 Phylloxera. One species of the last named genus lives partly on the 

 leaves, where it forms true galls, and partly on the roots, where it does 

 not form true galls. 



I. am unacquainted with the species of Adelges, but believe they pro- 

 duce swellings on the twigs, chiefly of pine trees. 



Genus Eriosoma (Schizoneura). 



The species of this genus do not usually, if ever, produce true galls, 

 that is, galls in which they reside, but are almost invariably found on the 

 bark of the trunk, branches or roots, where they produce a roughened 

 condition, little pimples, or even knotty excrescences or swellings. Their 

 wings are erect in repose, in the form of a steep roof above the abdomen; 

 the rib-vein of the fore wings emits three oblique branches similar to those 

 of the typical species already described, but the third or outer branch is 

 only once forked, and is often obsolete or indistinct at its base (see V., 

 fig. 3) ; the hind wings have the rib-vein near the front margin, which 

 gives off on the posterior side but one branch. The abdomen is without 

 any honey-tubes, and from the pores of the body there is usually secreted 

 a white, cottony or downy substance, with which the young and apterous 

 individuals are more or less covered. The summer broods consist, as the 

 previous species, chiefly of females, which otherwise produce living young 

 without the intervention of the male. 



{^Eriosoma lanigera, Hausm. The Woolly Aphis of the Apple-tree, 

 68. ' "American Blight," etc. 



i^ Pemphigus pyri, Fitch. The Apple-root Plant-louse. 



I do not give these two names as synonyms of the same species, but 

 mention them together because, by some, they are considered as varieties 

 of one species, while by others they are treated as distinct. As I pro- 

 pose to discuss this point more fully at another time, I will here mention 

 only the more prominent facts relating to their history, habits, nomencla- 

 ture and characteristics, leaving the reader to form his own conclusions. 

 For convenience, but without intending thereby to imply a specific dis- 

 tinction, I will use the name "Woolly Aphis," to designate the E. lanigera, 

 or trunk and branch inhabiting type; and "Apple-root louse," or simply 

 " Root-louse," to designate the P. pyri, or root-inhabiting type. 



The E. lanigera, or Woolly Aphis, was first described and scientifically 

 named by Hausmann, in 1801, as infesting the apple trees of Germany. 

 According to Serville and Amyot, it was unknown in Europe until 1787, 

 at which time it was first seen in England, having been imported that 

 year from North America. Tougard (Ann. Soc. d'Hort. de Paris) asserts 

 that it was unknown in Belgium previous to 1829. The same authors also 

 assert that it was unknown in France previous to 181 2. Harris, relying 

 upon the authority of Salisbury, (" Hints on Orchards,") asserts that it 

 was known to French gardeners for a long time previous to the earliest 

 of these dates. 



